System and method for detecting and characterizing vibrating targets

Abstract

A method and system for processing radar return signals reflected from a vibrating target to determine the actual vibration frequency and to isolate a characteristic vibration of the vibrating target, including an oscillation signature function (OSF). A radar signal processor receives a stabilized phase history which includes frequency components, namely an FM sideband corresponding to a modulation imparted upon a reflected radar return signal by the vibrating target. The radar signal processor detects the FM sideband and determines a candidate vibration frequency. The stabilized phase history is filtered at a phase rotation based on the candidate vibration frequency to isolate the OSF and to determine the actual vibration frequency. To distinguish the nearly identical frequency spectra produced by vibrating targets which vibrate at multiples of the radar system folding frequency, the stabilized input signal is further filtered at phase rotations corresponding to the candidate vibration frequency plus or minus multiples of the radar system folding frequency. By comparing the characteristic vibration or oscillation signature function with known information, the type of vibrating target, the identity of the vibrating target, and/or the state of the vibrating target can be determined. Further, the radar system can detect the actual vibration frequency and characteristic vibration of vibrating targets directly from the stabilized phase history prior to performing any image processing.

What is claimed is: 
     
       1. A method for determining a vibration frequency of a vibrating target comprising the steps of: detecting a frequency sideband in a stabilized phase history of a reflected return signal, said frequency sideband representing modulation imparted by the vibrating target; and   determining said vibration frequency of the vibrating target based on said detected frequency sideband, comprising the steps of: determining an offset vibration frequency from DC of said detected frequency sideband, and   filtering said stabilized phase history at a phase rotation corresponding to said offset vibration frequency to isolate a characteristic vibration and to verify that said offset vibration frequency is an actual vibration frequency of said vibrating target.     
     
     
       2. The method according to claim 1, wherein said offset vibration frequency constitutes a candidate vibration frequency of said vibrating target and said filtering step filters said stabilized phase history at a phase rotation corresponding to said candidate vibration frequency and at other selected phase rotations corresponding to other potential vibration frequencies; and further comprising the step of detecting a coherent signal after said filtering, said coherent signal being representative of characteristic vibration of said vibrating target at a phase rotation corresponding to the actual vibration frequency of the vibrating target. 
     
     
       3. The method according to claim 1, wherein said offset vibration frequency constitutes a candidate vibration frequency of said vibrating target and said filtering step filters said stabilized radar return signal at phase rotations corresponding to said candidate vibration frequency and to said candidate vibration frequency plus or minus multiples of a folding frequency associated with a carrier signal in said reflected return signal; and further comprising the step of detecting a coherent signal after said filtering, said coherent signal being representative of characteristic vibration of said vibrating target at a phase rotation corresponding to the actual vibration frequency of the vibrating target, whereby, said characteristic vibration and said actual vibration frequency of the vibrating target are detected regardless of whether the vibrating target has aliased at the offset vibration frequency. 
     
     
       4. The method according to claim 1, wherein said vibration frequency is determined from said stabilized phase history prior to imaging. 
     
     
       5. A method for isolating a characteristic vibration of a vibrating target comprising the steps of: detecting a frequency sideband in a stabilized phase history of a reflected return signal, said frequency sideband representing modulation imparted by the vibrating target;   determining at least one candidate vibration frequency based on said frequency sideband; and   filtering said stabilized phase history at a phase rotation corresponding to an actual vibration frequency of the vibrating target to isolate said characteristic vibration of the vibrating target, said filtering being based on said at least one candidate vibration frequency determined in said determining step.   
     
     
       6. The method according to claim 5, further comprising the step of comparing said isolated characteristic vibration with predetermined characteristic vibration information, whereby, at least one of the vibrating target type, identity, or state of vibration can be recognized. 
     
     
       7. A method according to claim 5, wherein said determining step further comprises determining a candidate vibration frequency comprising an offset vibration frequency from DC of said detected frequency sideband and said filtering step distinguishes between vibrating targets which alias at said offset vibration frequency by filtering said stabilized radar return signal at phase rotations corresponding to said candidate vibration frequency and to said candidate vibration frequency plus or minus multiples of a predetermined folding frequency associated with a carrier signal in said reflected return signal. 
     
     
       8. A signal processor for determining the vibration frequency of a vibrating target from a stabilized phase history of a return signal reflected from the vibrating target comprising: means for detecting a frequency sideband in said stabilized phase history, said detected frequency sideband representing modulation imparted by the vibrating target; and   means for determining said vibration frequency of the vibrating target based on said frequency sideband detected by said frequency sideband detecting means, wherein said vibration frequency determining means comprises: means for determining all offset vibration frequency from DC of said detected frequency sideband: and     means for filtering said stabilized phase history at a phase rotation corresponding to said offset vibration frequency to isolate a characteristic vibration and to verify that said offset vibration frequency is an actual vibration frequency of said vibrating target.   
     
     
       9. The signal processor according to claim 8, wherein said frequency sideband detecting means comprises: means for low pass filtering said stabilized phase history at a bandwidth substantially equal to a pulse repetition frequency of a carrier signal in said reflected return signal, and providing an output signal representative thereof;   means for decimating said output signal from said low pass filtering means at a sampling rate substantially equal to said pulse repetition frequency and providing a decimated signal representative thereof; and   means for detecting an FM vibration sideband in said decimated signal.   
     
     
       10. The signal processor according to claim 8, wherein said vibration frequency determining means further comprises means for filtering said stabilized phase history at a phase rotation corresponding to said offset vibration frequency to isolate a characteristic vibration and to verify that said offset vibration frequency is the actual vibration frequency of said vibrating target. 
     
     
       11. The signal processor according to claim 8, wherein said offset vibration frequency constitutes a candidate vibration frequency of said vibrating target and said filtering means filters said stabilized phase history at a phase rotation corresponding to said candidate vibration frequency and at other selected phase rotations corresponding to other potential vibration frequencies; and further comprising means for detecting a coherent signal output from said filtering means, said coherent signal being representative of characteristic vibration of said vibrating target at a phase rotation corresponding to the actual vibration frequency of the vibrating target.   
     
     
       12. The signal processor according to claim 8, wherein said offset vibration frequency constitutes a candidate vibration frequency of said vibrating target and said filtering means filters said stabilized phase history at phase rotations corresponding to said candidate vibration frequency and to said candidate vibration frequency plus or minus multiples of a folding frequency associated with a carrier signal in said reflected return signal; and further comprising means for detecting a coherent signal output from said filtering means, said coherent signal being representative of characteristic vibration of said vibrating target at a phase rotation corresponding to the actual vibration frequency of the vibrating target, whereby, said characteristic vibration and said actual vibration frequency of the vibrating target are detected regardless of whether the vibrating target has aliased at the offset vibration frequency.   
     
     
       13. The signal processor according to claim 12, wherein said filtering means comprises: a calculator means for calculating filter coefficients corresponding to said candidate vibration frequency and to said candidate vibration frequency plus or minus multiples of said folding frequency; and   a matched filter bank means comprising a plurality of filters for filtering said stabilized phase history at phase rotations according to said filter coefficients calculated by said calculator means.   
     
     
       14. The signal processor according to claim 8, wherein said stabilized phase history is provided by a radar system prior to imaging said stabilized phase history. 
     
     
       15. A detection system for isolating a characteristic vibration of a vibrating target comprising: a receiver means for providing a stabilized phase history of a return signal reflected from said vibrating target;   means for detecting a frequency sideband in said stabilized phase history provided by said receiver means, said frequency sideband representing modulation imparted by the vibrating target;   means for determining at least one candidate vibration frequency based on said frequency sideband detected by said detecting means; and   means for filtering said stabilized phase history at a phase rotation corresponding to an actual vibration frequency of the vibrating target based on said at least one candidate vibration frequency determined by said candidate vibration frequency means to isolate said characteristic vibration.   
     
     
       16. The detection system according to claim 15, wherein said detection system is a radar system and said receiver means is a radar receiver receiving a reflected radar return signal. 
     
     
       17. The detection system according to claim 15, further comprising means for comparing said isolated characteristic vibration with predetermined characteristic vibration information, whereby, at least one of the vibrating target type, identity, or state of vibration can be recognized. 
     
     
       18. The radar system according to claim 15, wherein said frequency sideband detecting means detects an FM vibration sideband;   said candidate vibration frequency determining means determines an offset vibration frequency from DC of said FM vibration sideband; and   said filtering means discriminates between vibrating targets which alias at said offset vibration frequency by filtering said stabilized phase history at phase rotations corresponding to said offset vibration frequency and to said offset vibration frequency plus or minus multiples of a folding frequency associated with a carrier signal in said stabilized phase history.   
     
     
       19. An oscillation signature function detector for isolating an oscillation signature function of a vibrating target imparted on a reflected return signal comprising: low pass filter means for receiving a stabilized complex phase history which includes said oscillation signature function, filtering said stabilized complex phase history at a bandwidth substantially equal to a pulse repetition frequency associated with a carrier signal in said reflected return signal, and providing an output representative thereof;   decimator means for decimating said output signal from said low pass filter means at a sampling rate substantially equal to said pulse repetition frequency and providing an output signal representative thereof;   detecting means for processing said output signal from said decimator means to detect an FM vibration sideband corresponding to the oscillation signature function imparted by the vibrating target and to determine a candidate vibration frequency by detecting an offset vibration frequency from DC of said detected FM vibration sideband;   calculator means for calculating matched filter coefficients based on said candidate vibration frequency and at least one multiple of a folding frequency associated with said carrier signal pulse repetition frequency;   matched filter means for performing phase rotations on said stabilized phase history based on said respective matched filter coefficients calculated by said calculator means; and   coherency detector means for detecting a coherent, phase continuous output signal from said matched filter means to isolate said oscillation signature function.   
     
     
       20. A vehicle mounted detection system for isolating a characteristic vibration of a vibrating target comprising: a receiver means for providing a stabilized phase history of a return signal reflected from said vibrating target, said receiver means being mounted on a vehicle;   means for detecting a frequency sideband in said stabilized phase history provided by said receiver means, said frequency sideband representing modulation imparted by the vibrating target;   means for determining at least one candidate vibration frequency based on said frequency sideband detected by said detecting means; and   means for filtering said stabilized phase history at a phase rotation corresponding to an actual vibration frequency of the vibrating target based on said at least one candidate vibration frequency determined by said candidate vibration frequency means to isolate said characteristic vibration.   
     
     
       21. The vehicle mounted system according to claim 20, further comprising means for comparing said isolated characteristic vibration with predetermined characteristic vibration information, whereby, at least one of the vibrating target type, identity, or state of vibration can be recognized. 
     
     
       22. The vehicle mounted system according to claim 20, wherein said vehicle comprises an aircraft for detecting vibrating ground targets.